Add deprecation warnings for `webclient` listener and non-HTTP(S) `web_client_location`. (#11774)

This changes the behaviour of the root endpoint to redirect
directly to the configuration of `web_client_location` if it is
given an HTTP(S) URL.

5 files changed, 40 insertions, 28 deletions

diff --git a/changelog.d/11774.misc b/changelog.d/11774.misc
new file mode 100644
index 0000000000..136ba57f94
--- /dev/null
+++ b/changelog.d/11774.misc
@@ -0,0 +1 @@
+Deprecate support for `webclient` listeners and non-HTTP(S) `web_client_location` configuration.
diff --git a/docs/sample_config.yaml b/docs/sample_config.yaml
index 5908f262e5..1b86d0295d 100644
--- a/docs/sample_config.yaml
+++ b/docs/sample_config.yaml
@@ -74,13 +74,7 @@ server_name: "SERVERNAME"
 #
 pid_file: DATADIR/homeserver.pid
 
-# The absolute URL to the web client which /_matrix/client will redirect
-# to if 'webclient' is configured under the 'listeners' configuration.
-#
-# This option can be also set to the filesystem path to the web client
-# which will be served at /_matrix/client/ if 'webclient' is configured
-# under the 'listeners' configuration, however this is a security risk:
-# https://github.com/matrix-org/synapse#security-note
+# The absolute URL to the web client which / will redirect to.
 #
 #web_client_location: https://riot.example.com/
 
@@ -310,8 +304,6 @@ presence:
 #   static: static resources under synapse/static (/_matrix/static). (Mostly
 #       useful for 'fallback authentication'.)
 #
-#   webclient: A web client. Requires web_client_location to be set.
-#
 listeners:
   # TLS-enabled listener: for when matrix traffic is sent directly to synapse.
   #
diff --git a/docs/upgrade.md b/docs/upgrade.md
index 30bb0dcd9c..f455d257ba 100644
--- a/docs/upgrade.md
+++ b/docs/upgrade.md
@@ -85,6 +85,17 @@ process, for example:
     dpkg -i matrix-synapse-py3_1.3.0+stretch1_amd64.deb
     ```
 
+# Upgrading to v1.51.0
+
+## Deprecation of `webclient` listeners and non-HTTP(S) `web_client_location`
+
+Listeners of type  `webclient` are deprecated and scheduled to be removed in
+Synapse v1.53.0.
+
+Similarly, a non-HTTP(S) `web_client_location` configuration is deprecated and
+will become a configuration error in Synapse v1.53.0.
+
+
 # Upgrading to v1.50.0
 
 ## Dropping support for old Python and Postgres versions
diff --git a/synapse/app/homeserver.py b/synapse/app/homeserver.py
index dd76e07321..7ef0fdf272 100644
--- a/synapse/app/homeserver.py
+++ b/synapse/app/homeserver.py
@@ -132,8 +132,10 @@ class SynapseHomeServer(HomeServer):
         self._module_web_resources_consumed = True
 
         # try to find something useful to redirect '/' to
-        if WEB_CLIENT_PREFIX in resources:
-            root_resource: Resource = RootOptionsRedirectResource(WEB_CLIENT_PREFIX)
+        if self.config.server.web_client_location_is_redirect:
+            root_resource: Resource = RootOptionsRedirectResource(
+                self.config.server.web_client_location
+            )
         elif STATIC_PREFIX in resources:
             root_resource = RootOptionsRedirectResource(STATIC_PREFIX)
         else:
@@ -262,15 +264,15 @@ class SynapseHomeServer(HomeServer):
             resources[SERVER_KEY_V2_PREFIX] = KeyApiV2Resource(self)
 
         if name == "webclient":
+            # webclient listeners are deprecated as of Synapse v1.51.0, remove it
+            # in > v1.53.0.
             webclient_loc = self.config.server.web_client_location
 
             if webclient_loc is None:
                 logger.warning(
                     "Not enabling webclient resource, as web_client_location is unset."
                 )
-            elif webclient_loc.startswith("http://") or webclient_loc.startswith(
-                "https://"
-            ):
+            elif self.config.server.web_client_location_is_redirect:
                 resources[WEB_CLIENT_PREFIX] = RootRedirect(webclient_loc)
             else:
                 logger.warning(
diff --git a/synapse/config/server.py b/synapse/config/server.py
index 5010266b69..f200d0c1f1 100644
--- a/synapse/config/server.py
+++ b/synapse/config/server.py
@@ -259,7 +259,6 @@ class ServerConfig(Config):
             raise ConfigError(str(e))
 
         self.pid_file = self.abspath(config.get("pid_file"))
-        self.web_client_location = config.get("web_client_location", None)
         self.soft_file_limit = config.get("soft_file_limit", 0)
         self.daemonize = config.get("daemonize")
         self.print_pidfile = config.get("print_pidfile")
@@ -506,8 +505,17 @@ class ServerConfig(Config):
                     l2.append(listener)
             self.listeners = l2
 
-        if not self.web_client_location:
-            _warn_if_webclient_configured(self.listeners)
+        self.web_client_location = config.get("web_client_location", None)
+        self.web_client_location_is_redirect = self.web_client_location and (
+            self.web_client_location.startswith("http://")
+            or self.web_client_location.startswith("https://")
+        )
+        # A non-HTTP(S) web client location is deprecated.
+        if self.web_client_location and not self.web_client_location_is_redirect:
+            logger.warning(NO_MORE_NONE_HTTP_WEB_CLIENT_LOCATION_WARNING)
+
+        # Warn if webclient is configured for a worker.
+        _warn_if_webclient_configured(self.listeners)
 
         self.gc_thresholds = read_gc_thresholds(config.get("gc_thresholds", None))
         self.gc_seconds = self.read_gc_intervals(config.get("gc_min_interval", None))
@@ -793,13 +801,7 @@ class ServerConfig(Config):
         #
         pid_file: %(pid_file)s
 
-        # The absolute URL to the web client which /_matrix/client will redirect
-        # to if 'webclient' is configured under the 'listeners' configuration.
-        #
-        # This option can be also set to the filesystem path to the web client
-        # which will be served at /_matrix/client/ if 'webclient' is configured
-        # under the 'listeners' configuration, however this is a security risk:
-        # https://github.com/matrix-org/synapse#security-note
+        # The absolute URL to the web client which / will redirect to.
         #
         #web_client_location: https://riot.example.com/
 
@@ -1011,8 +1013,6 @@ class ServerConfig(Config):
         #   static: static resources under synapse/static (/_matrix/static). (Mostly
         #       useful for 'fallback authentication'.)
         #
-        #   webclient: A web client. Requires web_client_location to be set.
-        #
         listeners:
           # TLS-enabled listener: for when matrix traffic is sent directly to synapse.
           #
@@ -1349,9 +1349,15 @@ def parse_listener_def(listener: Any) -> ListenerConfig:
     return ListenerConfig(port, bind_addresses, listener_type, tls, http_config)
 
 
+NO_MORE_NONE_HTTP_WEB_CLIENT_LOCATION_WARNING = """
+Synapse no longer supports serving a web client. To remove this warning,
+configure 'web_client_location' with an HTTP(S) URL.
+"""
+
+
 NO_MORE_WEB_CLIENT_WARNING = """
-Synapse no longer includes a web client. To enable a web client, configure
-web_client_location. To remove this warning, remove 'webclient' from the 'listeners'
+Synapse no longer includes a web client. To redirect the root resource to a web client, configure
+'web_client_location'. To remove this warning, remove 'webclient' from the 'listeners'
 configuration.
 """